Impurities and electronic localization in graphene bilayers

We analyze the electronic properties of bilayer graphene with Bernal stacking and a low concentration of adatoms. Assuming that the host bilayer lies on top of a substrate, we consider the case where impurities are adsorbed only on the upper layer. We describe non-magnetic impurities as a single orbital hybridized with carbon's pz states. The effect of impurity doping on the local density of states with and without a gated electric field perpendicular to the layers is analyzed. We look for Anderson localization in the different regimes and estimate the localization length. In the biased system, the field induced gap is partially filled by strongly localized impurity states. Interestingly, the structure, distribution and localization length of these states depend on the field polarization.Comment: 7 pages, 6 figure

Contact with nature and children's restorative experiences: An eye to the future

This article offers an overview of what has been done until now on restorative research with children and opens up new inquires for future research. Most of the work has studied children''s exposure to nature and the restorative benefits this contact provides, focusing on the renewal of children''s psychological resources. The paper begins with an introduction to children''s current tendency toward an alienation from the natural world and sets out the objectives of the article. It is followed by four main sections. The first two sections report on what we already know in this research area, distinguishing between children with normal mental capabilities and those suffering from attention-deficit hyperactivity disorder (ADHD). The findings gathered in these sections suggest that children''s contact with nature improves their mood and their cognitive functioning, increases their social interactions and reduces ADHD symptoms. The next section describes five suggestions for future research: (1) the need for considering the relational dynamics between the child and the environment in restoration research, and the concept of constrained restoration; (2) the possibility of restorative needs arising from understimulation; (3) the importance of considering children''s social context for restoration; (4) the relationship between restoration and pro-social and pro-environmental behaviors; and (5) children''s restorative environments other than nature. We close by making some final remarks about the importance of restoring daily depleted resources for children''s healthy functioning

Bilayer graphene under pressure: Electron-hole Symmetry Breaking, Valley Hall Effect, and Landau Levels

The electronic structure of bilayer graphene under pressure develops very interesting features with an enhancement of the trigonal warping and a splitting of the parabolic touching bands at the K point of the reciprocal space into four Dirac cones, one at K and three along the T symmetry lines. As pressure is increased, these cones separate in reciprocal space and in energy, breaking the electron-hole symmetry. Due to their energy separation, their opposite Berry curvature can be observed in valley Hall effect experiments and in the structure of the Landau levels. Based on the electronic structure obtained by Density Functional Theory, we develop a low energy Hamiltonian that describes the effects of pressure on measurable quantities such as the Hall conductivity and the Landau levels of the system.Comment: 11 pages, 9 figure

Normative Influences on Adolescents’ Self-Reported Pro-Environmental Behaviors: The Role of Parents and Friends

Pro-environmental behavioral patterns are influenced by relevant others’ actions and expectations. Studies about the intergenerational transmission of environmentalism have demonstrated that parents play a major role in their children’s pro-environmental actions. However, little is known about how other social agents may shape youth’s environmentalism. This cross-sectional study concentrates on the role that parents and peers have in the regulation of 12- to 19-year-olds’ pro-environmental behaviors. We also consider the common response bias effect by examining the associations between parents, peers, and adolescents’ pro-environmentalism in two independent data sets. Data Set 1 (N = 330) includes adolescents’ perceptions of relevant others’ behaviors. Data Set 2 (N = 152) includes relevant others’ self-reported pro-environmental behavior. Our results show that parents’ and peers’ descriptive and injunctive norms have a direct effect on adolescents’ pro-environmental behavior and an indirect one, through personal norms. Adolescents seem to be accurate in the perception of their close ones’ environmental actions

Towards a definition of a CRM system life-cycle

In recent years, the interest on research in Customer Relationship Management (CRM) systems has grown notoriously. Many authors have made individual proposals of interesting topics to be researched around CRM systems, but no overarching research agenda has yet been proposed. Based upon a recent research literature review that we have undertaken, which includes several real case studies conducted in order to learn from CRM experience within specific companies and industries, we propose and detail what appears to be a natural CRM Systems Life-cycle. Although a more focussed cycle has been mentioned for CRM systems implementations, we propose and define in detail a CRM Systems Life-cycle which covers other phases preceding and following implementation. We believe that such a well-defined cycle may help in future proposals of research agendas around CRM systems, as well as in the contextualization of more specific research themes.Postprint (published version

The new Wolf-Rayet binary system WR62a

Context. A significant number of the Wolf-Rayet stars seem to be binary or multiple systems, but the nature of many of them is still unknown. Dedicated monitoring of WR stars favours the discovery of new systems. Aims. We explore the possibility that WR62a is a binary system. Methods. We analysed the spectra of WR62a, obtained between 2002 and 2010, to look for radial-velocity and spectral variations that would suggest there is a binary component. We searched for periodicities in the measured radial velocities and determined orbital solutions. A period search was also performed on the "All-Sky Automated Survey" photometry. Results. We find that WR62a is a double-lined spectroscopic binary with a WN5 primary star and an O 5.5-6 type secondary component in orbit with a period of 9.1447 d. The minimum masses range between 21 and 23 Mo for the WN star and between 39 and 42 Mo for the O-type star, thus indicating that the WN star is less massive than the O-type component. We detect a phase shift in the radial-velocity curve of the He II 4686 emission line relative to the other emission line curves. The equivalent width of this emission line shows a minimum value when the WN star passes in front of the system. The analysis of the ASAS photometry confirms the spectroscopic periodicity, presenting a minimum at the same phase.Comment: 7 pages, 8 figures, accepted for publication in A&

Experimental approval of the extended flat bands and gapped subbands in rhombohedral multilayer graphene

Graphene layers are known to stack in two stable configurations, namely ABA or ABC stacking, with drastically distinct electronic properties. Unlike the ABA stacking, little has been done to experimentally investigate the electronic properties of ABC graphene multilayers. Here, we report the first magneto optical study of a large ABC domain in a graphene multilayers flake, with ABC sequences exceeding 17 graphene sheets. The ABC-stacked multilayers can be fingerprinted with a characteristic electronic Raman scattering response, which persists even at room temperatures. Tracing the magnetic field evolution of the inter Landau level excitations from this domain gives strong evidence to the existence of a dispersionless electronic band near the Fermi level, characteristic of such stacking. Our findings present a simple yet powerful approach to probe ABC stacking in graphene multilayer flakes, where this highly degenerated band appears as an appealing candidate to host strongly correlated states.Comment: 8 pages, 4 figure